1. Field of the Invention
This invention relates to an ophthalmologic apparatus comprising a slit light projecting optical system for projecting a slit beam of light onto the cornea of a subject's eye and means for measuring the thickness of the cornea.
2. Description of the Related Art
Conventionally, an ophthalmologic apparatus has been known which comprises a slit light projecting optical system for obliquely projecting a slit beam of light onto the cornea of a subject's eye and a light receiving optical system for receiving light rays reflected from the cornea and which measures the thickness of the cornea according to received-light information of the light receiving optical system.
This type of ophthalmologic apparatus not only measures the thickness of the cornea according to the received light information but also calculates the distance between the cornea and a body of the apparatus according to the received light information so as to adjust alignment of a mechanical optical axis (in Z-direction) of the apparatus body (Japanese Patent Application No. Hei 5-99641).
However, in this ophthalmologic apparatus, a slit beam of light is used both for alignment in Z-direction and for measurement of the thickness of the cornea and, in addition, the width of the slit beam is made smaller to correctly measure the corneal thickness. Therefore, large disalignment (i.e., large positional deviation) of the mechanical optical axis of the apparatus body with respect to the cornea causes large deviation of the cornea-reflected light rays from a normal reflected direction. This makes it impossible that a photosensor of the light receiving optical system receives the reflected light rays. Accordingly, there is a disadvantage in that the direction in which the apparatus body is out of alignment cannot be detected, and thus the apparatus body cannot be quickly moved in an appropriate direction.